2 types of sex determination
genotypic sex determination
temperature dependent sex determination
bipotential gonad
indifferent gonad that could be turned into either the testes or ovaries
what type of sex determination do amphibians have
genotypic sex determination
XX/XY
ZZ/ZW
heterogamety
when the sex chromosomes are different
ex: male mammals are XY
what type of heterogamety is the ancestral condition and which has evolved
ancestral: female
evolved multiple times: male
reproductive cycles (2)
seasonal reproduction
aseasonal reproduction
seasonal reproduction
most species in temperate zones
only in later winter, early spring
only during summer
only during autumn
in tropics: wet season breeders (temperature and rainfall)
aseasonal reproduction
continuous reproductive cycles
some anurans in relatively aseasonal tropical habitats
spermatophores in salamanders
males
like a capsule left behind:
made of cloacal glands
outer layer is a mass of sperm cells
internal fertilization: promotes female parental care
how can female salamanders store sperm
with the spermathecae
tubules in wall of cloaca
sperm is stored for later fertilization
amplexus in anurans (3)
mating behavior in which male frog grasps the female from behind to bring their cloacae into close proximity and aid fertiliztion
inguinal amplexus
axillary amplexus (majority of anurans)
cephalic amplexus
which amplexus type is the ancestral condition
inguinal amplexus
which type of amplexus is only found in dendrobatids (poison dart frogs)
cephalic amplexus
nuptial pad in anurans
assists in amplexus for the male to grasp the female more firmly
phalloduem function
caecilians
extension of male cloaca that assists in internal fertilization
hybridogenesis
genome of the female parent that passes unchanged from one generation to the next
paternal genome discarded and gametes produced by hybrid female contain only maternal genome
intermediate phenotype = hybrid female + parental species male
kleptogenesis and the 3 possibilities
females that steal genomes from males of other species
has 3 outcomes:
sperm initiates development of embryo but sperm’s genetic material is not incorporated into embryo
sperm sometimes incorporates but resulting offspring has a higher ploidy (chromosomes) level
sperm genome replaces one of the original genomes in the hybrid offspring
ex: ambystoma species
oviparity in caecilians (2)
aquatic larvae
direct development with female as parental care
viviparity in caecilians
yolk and maternal secretions
11-12 months
modes of oviparity in salamanders (3)
mode 1: pond breeding
mode 2: stream breeding
mode 3: nonaquatic eggs (has several subcategories)
egg sacs of salamanders in mode 1
pond breeding
more clustered together in a giant ball
egg sacs of salamanders in mode 2
stream breeding
more tube like sacs that are attached to substrate
egg sacs of salamanders in mode 3
terrestrial eggs
laid in shallow depressions or attached to leaves
direct development with no water required or a small amount of water
viviparity in salamanders
very limited
some populations where female fertilizes multiple eggs
some populations with few eggs and unfertilized ones get eaten by fertilized ones (offspring)
some populations with only 2 eggs fertilized
ex: european fire salamander
types of oviposition in anurans (5)
various arrangements of independent eggs
3D arrangements
floating arrangements
foam nests
linear arrangements
eggs and larvae in water (anurans)
ancestral form
cluster of eggs in water with arrangement dependent on O2 levels
cold: more O2, more clumped together
warm: less O2, film of eggs in single layer on top of water
foam nests (anurans)
mucus mixed with water and the frog paddles its feet to foam it
shift from ponds and streams (anurans)
avantages:
less predators
disadvantages:
less food
offspring subsist on yolk in eggs instead
aboreal water (anurans)
tree holes
ex: bromeliads where a single egg gets places in the direct center
eggs on land where larvae develop in water (anurans)
mud nests, water sac on bottom of leaf
rain breaks mud nest open
in water sac, eggs are out of predators way and they simply drop out when ready
non aquatic larvae (anurans)
direct development where development occurs entirely in the egg
no metamorphosis (tadpole stage)
ex: australian turtle frog
parental care in anurans (4)
egg attendance
transport of eggs
attendance of tadpoles and/or young
transport of tadpoles and/or young, and feeding of tadpoles
ex of a frog that transports its tadpoles
dendrobatids
transport tadpoles from terrestrial oviposition site to a body of water
viviparity in anurans (2)
lecithotrophy
matrotrophy
includes 9 species between the 2 types
lecithotrophy
yolk reserves
7 species
matrotrophy
maternal secretions
2 species
benefits of direct development and viviparity in anurans (2)
large eggs, large yolk reserves
not dependent on standing water
costs of direct development and viviparity in anurans (3)
reduction in total reproductive output
lower clutch size
increased vulnerability to predation
benefits of parental care in anurans (4)
decrease in pathogens (cleaner eggs)
decrease in predation
increase in aeration
prevents desiccation (keeps moisture)
costs of parental care in anurans (3)
reduced reproductive output
decrease food intake
reduced survival of the parent
what is the relationship between egg size and clutch size (anurans)
quality: larger egg size, smaller clutch size
direct development, parental care
quantity: smaller egg size, larger clutch size
species that lay eggs water, aquatic larval development
how does resource variability influence egg and clutch size (anurans)
excess food:
larvae hatch from large eggs, metamorphose sooner in larger in size
limited food:
larvae hatch from small eggs, metamorphose earlier
how does environmental variability influence egg and clutch size (anurans)
favorable environment:
small eggs might survive, female could increase fitness by producing many small eggs
unpredictable environment:
produce a range of egg sizes that might increase the change that some offspring will survive
larval development in caecilians
no aquatic larval stage
those with aquatic stage are relatively short and their external gills are lost quickly
larval development/metamorphosis in salamanders
pond dwelling larvae keep tail fin and lateral line
stream dwelling larvae lose tail fin and lateral line
lateral line in pond dwelling salamander larvae
a line of sensory receptors
larval development/metamorphosis in anurans (4)
egg fertilized
external gills develop
early stage: tadpoles subsist largely on yolk in
mouth development
late stage: tadpoles feed (are herbivores)
limb development
adult stage: primarily carnivorous
how can environmental variation alter life history traits in anurans
breeding in rain pool vs longer lasting temporary pond vs longer lasting pond has effects on duration of larval stage
rain pool: shortest (8 days)
longer lasting pond: longest (7 weeks)
how does larval body size > minimum body size trigger either additional growth or metamorphosis in the wilbur collins model
not >: additional growth
yes >: decide if larval body size > max body size
how does larval body size > maximum body size trigger either additional growth or metamorphosis in the wilbur collins model
not >: size specific growth rate
yes >: metamorphosis
how does size specific growth rate trigger either additional growth or metamorphosis in the wilbur collins model
not: metamorphosis
yes: additional growth
how does population density influence growth in anurans
smaller density: grow larger
higher density: grow smaller (competition)
how can environmental varation (duration of aquatic environments) influence the expression of paedomorphosis
shorter duration (temporary pond): less paedomorphic
longer duration (longer lasting pond): more paedomorphic
how can environmental variation (absence of light) influence the expression of paedomorphosis
more paedomorphic in cave dwelling (light absence) species